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REV. B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. a 4–20 mA Transmitter AD694
FEATURES
4–20 mA, 0–20 mA Output Ranges Precalibrated Input Ranges:
0 V to 2 V, 0 V to 10 V
Precision Voltage Reference Programmable to 2.000 V or 10.000 V Single or Dual Supply Operation Wide Power Supply Range: 4.5 V to 36 V Wide Output Compliance Input Buffer Amplifier Open-Loop Alarm Optional External Pass Transistor to Reduce Se lf-Heating Errors 0.002% Typ Nonlinearity PRODUCT DESCRIPTION The AD694 is a monolithic current transmitter that accepts high level signal inputs to drive a standard 4–20 mA current loop for the control of valves, actuators, and other devices com- monly used in process control. The input signal is buffered by an input amplifier that can be used to scale the input signal or buffer the output from a current mode DAC. Precalibrated in- put spans of 0 V to 2 V and 0 V to 10 V are selected by simple pin strapping; other spans may be programmed with external resistors. The output stage compliance extends to within 2 V of V S and its special design allows the output voltage to extend below common in dual supply operation. An alarm warns of an open 4–20 mA loop or noncompliance of the output stage. Active laser trimming of the AD694’s thin film resistors results in high levels of accuracy without the need for additional adjust- ments and calibration. An external pass transistor may be used with the AD694 to off-load power dissipation, extending the temperature range of operation. The AD694 is the ideal building block for systems requiring noise immune 4–20 mA signal transmission to operate valves, actuators, and other control devices, as well as for the transmis- sion of process parameters such as pressure, temperature, or flow. It is recommended as a replacement for discrete designs in a variety of applications in industrial process control, factory automation, and system monitoring. The AD694 is available in hermetically sealed, 16-pin CERDIP and plastic SOIC, specified over the –40 °C to +85°C industrial temperature range, and in a 16-pin plastic DIP, specified over the 0°C to +70°C temperature range. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 2002 PRODUCT HIGHLIGHTS 1. The AD694 is a complete voltage in to 4–20 mA out current transmitter. 2. Pin programmable input ranges are precalibrated at 0 V to 2 V and 0 V to 10 V. 3. The input amplifier may be configured to buffer and scale the input voltage, or to serve as an output amplifier for current output DACs. 4. The output voltage compliance extends to within 2 V of the positive supply and below common. When operated with a
5 V supply, the output voltage compliance extends 30 V be-
low common. 5. The AD694 interfaces directly to 8-, 10-, and 12-bit single supply CMOS and bipolar DACs. 6. The 4 mA zero current may be switched on and off with a TTL control pin, allowing 0–20 mA operation. 7. An open collector alarm warns of loop failure due to open wires or noncompliance of the output stage. 8. A monitored output is provided to drive an external pass transistor. The feature off-loads power dissipation to extend the temperature range of operation and minimize self-heating error.
AD694–SPECIFICATIONS Model AD694JN/AQ/AR AD694BQ/BR Min Typ Max Min Typ Max Unit INPUT CHARACTERISTICS Input Bias Current Either Input, TMIN to TMAX 1.5 5 1.5 5 nA Offset Current, TMIN to TMAX ± 0.1 /H115501 ± 0.1 /H115501 nA Offset Current Drift ± 1.0 ± 5.0 ± 1.0 ± 5.0 pA/ °C Input Impedance 5 5 MΩ OUTPUT CHARACTERISTICS Operating Current Range 0 23 0 23 mA Specified Performance 4 20 4 20 mA Output Voltage Compliance VS –36 V VS –2 V V S –36 V VS 2 V V Output Impedance, 4–20 mA 40.0 50.0 40.0 50.0 M Ω Current Limit (@ 2 × FS Overdrive 24 44 24 44 mA Slew Rate 1.3 1.3 mA/µs SPAN AND ZERO ACCURACY 1 4 mA Offset Error @ 0 V Input 2 Error from 4.000 mA, 4 mA On ± 10 /H1155020 ± 5 /H1155010 µA Error from 0.000 mA, 4 mA Off 0 +10 +20 0+ 5 +10 µA TMIN to TMAX ± 10 /H1155040 ± 5 /H1155020 µA Trim Range, 4 mA Zero 2.0 4.8 2.0 4.8 mA Span Nominal Transfer Function Input FS = 2 V 8.0 8.0 mA/V Input FS = 10 V 1.6 1.6 mA/V Transfer Function Error from Nom, Input FS = 2 V, 10 V ± 0.1 /H115500.3 ± 0.05 /H115500.15 % of Span TMIN to TMAX ± 0.002 ± 0.005 ± 0.001 /H115500.0025 % of Span/°C Nonlinearity3 ± 0.005 /H115500.015 ± 0.001 /H115500.005 % of Span 4 mA On: Max Pin 9 Voltage 0.8 0.8 V 4 mA Off: Min Pin 9 Voltage 3.0 2.5 3.0 2.5 V VOLTAGE REFERENCE TMIN to TMAX 4 30 50 20 30 ppm/°C Output Current Source 5 5m A Sink 0.2 0.2 mA ALARM CHARACTERISTICS VCE(SAT) @ 2.5 mA 0.35 0.35 V Leakage Current /H115501 /H115501 µA Alarm Pin Current (Pin 10) 20 20 mA POWER REQUIREMENTS Specified Performance 24 24 V Operating Range 2 V FS, VREF = 2 V 4.5 36 4.5 36 V 2 V, 10 V FS, VREF = 2 V, 10 V 12.5 36 12.5 36 V Quiescent Current, 4 mA Off 1.5 2.0 1.5 2.0 mA TEMPERATURE RANGE Specified Performance 5 AD694AQ/BQ/AR/BR –40 +85 –40 +85 °C AD694JN 0 +70 0 +70 °C Operating AD694AQ/BQ/AR/BR –55 +125 –55 +125 °C AD694JN –40 +85 –40 +85 °C (@ +25/H11543C, RL = 250 /H9024, and VS = +24 V, unless otherwise noted.) REV. B–2–
Model AD694JN/AQ/AR AD694BQ/BR Min Typ Max Min Typ Max Unit BUFFER AMPLIFIER6 Input Offset Voltage Initial Offset ± 150 /H11550500 ± 50 /H11550500 µV TMIN to TMAX ± 2 ± 3 ± 2 ± 3 µV/°C vs. Supply 80 90 80 90 dB vs. Common Mode 80 90 80 90 dB Trim Range /H115502.5 ± 4.0 /H115502.5 ± 4.0 mV Frequency Response Unity Gain, Small Signal 300 300 kHz Input Voltage Noise (0.1 Hz to 10 Hz) 2 2 µV p-p Open-Loop Gain VO = +10 V, RL ≥ 10 kΩ 50 50 V/mV Output Voltage @ Pin 1, FB 1 Minimum Output Voltage 1.0 10 1.0 10 mV Maximum Output Voltage VS –2.5 V V S–2 V VS –2.5 V V S –2 V V NOTES 1The single supply op amps of the AD694, lacking pull down current, may not reach 0.000 V at their outputs. For this reason, span, offset, and nonlinearity are specified with the input amplifiers operating in their linear range. The input voltage used for the tests is 5 mV to 2 V and 5 mV to 10 V for the two precalibrated input ranges. Span and zero accuracy are tested with the buffer amplifier configured as a follower. 2Offset at 4 mA out and 0 mA out are extrapolated to 0.000 V input from measurements made at 5 mV and at full scale. See Note 1. 3Nonlinearity is specified as the maximum deviation of the output, as a % of span, from a straight line drawn through the endpoints of the transfer function. 4Voltage reference drift guaranteed by the Box Method. The voltage reference output over temperature will fall inside of a box whose length is determined by the temperature range and whose height is determined by the maximum temperature coefficient multiplied by the temperature span in degrees C. 5Devices tested at these temperatures with a pass transistor. Allowable temperature range of operation is dependent upon internal power dissipation. Absolute maximum junction and case temperature should not be exceeded. See section: “Power Dissipation Considerations.” 6Buffer amplifier specs for reference. Buffer amplifier offset and drift already included in Span and Zero accuracy specs above. Specifications subject to change without notice. Specifications shown in boldface are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality l evels. All min and max specifications are guaranteed, although only those shown in boldface are tested on all production units. AD694 –3–REV. B PIN CONFIGURATION (N, R, Q PACKAGE) ABSOLUTE MAXIMUM RATINGS Storage Temperature Range Maximum Case Temperature ORDERING GUIDE Temperature Package Model Range Option* AD694JN 0°C to 70°C N-16 AD694AQ –40°C to +85°CQ -16 AD694AR –40°C to +85°C R-16 AD694BQ –40°C to +85°CQ -16 AD694BR –40°C to +85°C R-16 *N = Plastic DIP; Q = CERDIP, R = SOIC Thermal Characteristics: Plastic (N) Package: θ JC = 50°C/Watt θCA (Still Air) = 85°C/Watt Cerdip (Q) Package: θJC = 30°C/Watt θCA (Still Air) = 70°C/Watt Plastic (R) Package: θJC = 27°C/Watt θCA (Still Air) = 73°C/Watt ESD Susceptibility All pins are rated for a minimum of 4000 V protection, except for Pins 2, 3 and 9 which are rated to survive a minimum of 1500 V. ESD testing conforms to Human Body Model. Always practice ESD prevention. No pin, other than I OUT (11) and ±Sig (2), (3) as noted, may be permitted to become more negative than Com (5). No pin may be permitted to become more positive than V S (13).
Figure 1. Functional Block Diagram sponsible for providing the 4 mA offset current signal. S. The Class A output of the amplifier appears at Pin 1 (FB). within 2.5 V of VS when the amplifier is operated as a follower. only as much as its internal 10 k Ω pulldown resistor allows. shifted signal across the 45 Ω resistor to get a current gain of 20. full-scale input for a 16 mA output span.
10 V force pin is connected to the base of the NPN, and the
S Of the part increases by approximately 0.7 V.
4.5 V SINGLE SUPPLY OPERATION
erence output of 2 V as described above. the buffer amplifier to buffer input signals. The AD694 is designed to be stable when driving resistive loads. Figure 3. Capacitor Utilized When Driving Nonresistive should connect to the NPN emitter instead of Pin 11. source a current to a point as low as 23.5 V below common.
0.7 V, the V
AD694 is operated with dual supplies, as shown in Figure 4. This will not reduce the voltage compliance of the output stage. sinking the external pass transistor is suggested.
Figure 13. Digital to 4–20 mA Interface Using a Current Steering DAC Figure 14. Single-Supply Digital Input to 4–20 mA Output the DAC will increase and the linearity will be degraded. put current of 3.2 mA to 20.8 mA. added which easily handles these types of low level signals. Figure 15. The AD694’s 2 V reference is used to provide a verter 2 volts positive, to match the “ground” of the in amp.
0 V to 2 V differential swing across V
Figure 15. Low Cost Sensor Transmitter
3 V source would result in a V
volt differential input from the sensor.
REV. B –13– OUTLINE DIMENSIONS 16-Lead Ceramic DIP-Glass Hermetic Seal Package [CERDIP] (Q-16) Dimensions shown in millimeters and (inches) 7.87 (0.3100) 5.59 (0.2200) PIN 1 0.13 (0.0051) MIN 2.03 (0.0799) MAX 8.13 (0.3201) 7.37 (0.2902) 0.38 (0.0150) 0.20 (0.0079) SEATING PLANE 5.08 (0.2000) MAX 21.34 (0.8402) MAX 3.81(0.1500) MIN 5.08 (0.2000) 3.18 (0.1252) 0.58 (0.0228) 0.36 (0.0142) 2.54 (0.1000) BSC 1.78 (0.0701) 0.76 (0.0299) 1.52 (0.0598) 0.38 (0.0150) CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN 16-Lead Plastic Dual-in-Line Package [PDIP] (N-16) Dimensions shown in millimeters and (inches) 1 8 PIN 1 21.34 (0.8402) 18.92 (0.7449) 7.11 (0.2799) 6.10 (0.2402) SEATING PLANE 1.52 (0.0598) MAX 0.56 (0.0220) 0.36 (0.0142) 4.06 (0.1598) 2.93 (0.1154) 2.54 (0.1000) BSC 1.77 (0.0697) 1.15 (0.0453) 3.30 (0.1299) MIN 4.95 (0.1949) 2.93 (0.1154) 0.38 (0.0150) 0.20 (0.0079) 8.25 (0.3248) 7.62 (0.3000) CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN 16-Lead Standard Small Outline Package [SOIC] Wide Body (R-16) Dimensions shown in millimeters and (inches) SEATING PLANE 0.30 (0.0118) 0.10 (0.0039) 0.51 (0.0201) 0.33 (0.0130) 2.65 (0.1043) 2.35 (0.0925) 1.27 (0.0500) BSC 16 9 10.65 (0.4193) 10.00 (0.3937) 7.60 (0.2992) 7.40 (0.2913)PIN 1 10.50 (0.4134) 10.10 (0.3976) 0.32 (0.0126) 0.23 (0.0091) 8/H11543 0/H11543 0.75 (0.0295) 0.25 (0.0098)/H11547 45/H11543 1.27 (0.0500) 0.40 (0.0157) COPLANARITY 0.10 CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN COMPLIANT TO JEDEC STANDARDS MS-013AA
–14– REV. B
Revision History
8/02—Data Sheet changed from REV. A to REV. B.
REV. B –15–
–16– C00817–0–8/02(B) PRINTED IN U.S.A.